1. Field of the Invention
The present invention relates to an X-ray image taking apparatus which makes modification of an image taking operation mode possible, and an operation control program thereof.
2. Related Background Art
Up to now, a film screen system where an intensifying screen and an X-ray photographic film has been widely used for an X-ray image taking operation aiming at a medical diagnosis. A film image which is given the X-ray image taking operation is hung on a schaukasten and is observed, and the film is designed so as to become in the contrast which is in a tone range of being easy to observe a diagnostic part. Nevertheless, when a image taking parameter shifts, overexposure and underexposure tend to easily arise, and hence, there is a possibility of having an adverse effect on a diagnosis.
It has been started in recent years that an X-ray digital image taking apparatus of adopting an FPD (Flat Panel Detector) as a plane sensor converting an X-ray image into an electrical signal proportional to the strength of X-rays is used. Since extracting a feature of an image with image processing technology, this image taking apparatus can solve a former problem of exposure adjustment and further has a function of enhancing diagnostic ability by image processing such as image enhancement.
When this kind of FPD is used, it is desirable to correct an offset since a noise component caused by a dark current is added to an image as the offset. In general, offset noise (FPN: fixed pattern noise) is expressed as a function of accumulation time of a sensor. As an offset correction method, as described in Japanese Patent Application Laid-Open No. 10-208016, there is a known method of storing a FPN image, corresponding to accumulation time inputted into the FPD, in memory and performing correction by subtracting the FPN image from a taken image.
Nevertheless, in the above-mentioned offset correction method, when a special image taking operation such as a long-time image taking operation is performed, a condition of the noise component caused by the dark current changes. Hence, since a device which performs behavior like a defective pixel appears, an image processing condition changes in automatic exposure adjustment. Therefore, since a correction error arises, manual adjustment becomes necessary, or there is a possibility of affecting a diagnosis.
Then, a method of changing the correction method by inputting an operating temperature change and operation time of FPD into a correction circuit is also known. Nevertheless, since this is implemented by hardware so as to be processed in real time, there is a problem of becoming expensive.